Oxalic Acid
in
Varroa Management
Randy Oliver
Revised 14 Jan 2016
(see notes under the slides)
Oxalic has a long history in Europe
Why Oxalic Acid?
Acids are much more
toxic to mites than to bees
Oxalic is the
strongest
organic acid
http://www.varroamilbe.ch/
There are speculative hypotheses as to why acids kill varroa, but no
definitive study.
Beekeeper Gerhard Bruning suspects that OA crystals are absorbed
through varroa’s sticky tarsal pads.
Safety to Humans
Oxalis
http://helios.hampshire.edu/~nlNS/mompdfs/oxalica
Typical treatment=
1 serving
per hive
Purchasing Oxalic Acid
Sold as
oxalic acid
dihydrate
“Wood Bleach”
Thanks to Brushy Mountain for registering oxalic!
Mixing Oxalic Syrup
Need to
weigh
Don’t use hard water
Use the exact dose!
“Hot”
4.2% w:v
“Medium”
3.2% w:v
“Weak”
2.5% w:v
OA crystals
1
0.75
0.6
Sucrose
10
10
10
Dist. Water
10
10
10
OA crystals
60g
45g
35g
Sucrose
600g
600g
600g
Dist. water
600ml
600ml
600ml
OA crystals
100g
75g
60g
Sucrose
1 kg
1 kg
1 kg
Dist. water
1 liter
1 liter
1 liter
OA crystals
232g
174g
139g
Sucrose
5 lb
5 lb
5 lb
Dist. water
2.5 qt
2.5 qt
2.5 qt
OA crystals
1112g (2lb 7oz)
834g (1lb 13.4oz)
667g (1lb 7.5oz)
Sucrose
25 lb
25 lb
25 lb
Dist. water
3 gal
3 gal
3 gal
Oxalic
strength→
Notes
Oxalic crystals must be
measured by weight. Sugar
and water are about the
same by weight or volume
(1 pint of either granulated
sugar or water weigh 1 lb)
Makes 1 liter
Treats about 20 colonies
Makes 1700ml
Treats about 33 colonies
Makes 1+ gallon
Treats about 75 colonies
Makes 5 gallons
Treats about 375 colonies
Oxalic acid crystals dissolve more readily in hot
water than in sugar solution.
Tip: dissolve the oxalic crystals in the indicated
amount of hot (150˚F) water before adding the
sugar.
After the oxalic crystals are fully dissolved, only
then stir in the sugar.
Storage
Store in the ‘fridge
Safety
Protect your eyes
Tastes like strong
lemonade
Carry baking
soda in water to
neutralize
Application
Must be applied directly
to bees’ bodies.
~5 mL per “seam” of
bees
1 tsp = 5 mL
Dribble, not spray
Calibrate pump
output
Hit both boxes
Tips:
Fill the garden sprayer only about ¼ full of
solution. This leaves a large air space, which
minimizes the fluctuation in pressure.
After you’ve dribbled a yard of hives, measure
how much syrup you’ve applied in total, and
divide by the number of hives. This will tell you
if you’re applying the correct amount.
Timing of Treatment
http://www.sbai.org.uk/
Oxalic won’t kill mites in the brood.
Note the
difference in
efficacy,
dependent
upon how
much brood is
present.
Oxalic gives poor efficacy if there is much brood present,
especially if drone brood is present.
Seasonality Best treatment windowsof Worker
Demographics
Fall treatment
Oxalic acid is, by far, most effective when colonies are broodless.
We use our fall oxalic dribble
as a last check on our
colonies before winter. I took
a step back from swapping
frames of honey from heavy
to lightweight hives to show
Eric and Ian dribbling oxalic in
the background.
We use our fall oxalic dribble
as a last check on our
colonies before winter.
Oxalic drops mites
for about 4 days.
Benefit against
nosema
Nosema infection after fall dribble of weak OA, 50mL/hive
Summer Treatment
•
Can be used on severely mite-stressed colonies to buy time.
•
Must be repeated at weekly intervals.
Colony about to
collapse
Formic or
thymol may be
too strong a
treatment
Summer
treatment—
3 weekly
applications.
Around 50% mite
reduction.
Induced Brood Break
Understand the timing!
Beekeepers in Italy create an induced brood break
during late summer by temporarily caging the queen
Understand the timing!
Cage the queen for 12 days
minimum. Then release her.
Treat 4-5 days later.
http://eberthoney.com/
Treat walkaway splits at 20 days.
Combine OA with requeening
Kill the old queen,
insert a queen
cell,
treat with OA 19
days later.
http://eberthoney.com/
http://eberthoney.com/
Cage the old queen for 2 weeks,
then remove her and introduce a new queen,
treat with OA 5 days later.
Treatment of Nucs
or Packages
A no brainer
Treat package bees or swarms shortly after
installation for a “clean start”
Treatment window for nucs
Doesn’t appear to harm queens
Graft #Queen(s) No. cells Day Graft date Sealed Incubator Nucs by Early ripe Typ mate Typ eggs Check/oxalic
Fri
3/9
3/13
3/16
3/18
3/19
3/28
3/31
4/6
Sat
3/10
3/14
3/17
3/19
3/20
3/29
4/1
4/7
Sun
3/11
3/15
3/18
3/20
3/21
3/30
4/2
4/8
Mon
3/12
3/16
3/19
3/21
3/22
3/31
4/3
4/9
Tue
3/13
3/17
3/20
3/22
3/23
4/1
4/4
4/10
Wed
3/14
3/18
3/21
3/23
3/24
4/2
4/5
4/11
Th
3/15
3/19
3/22
3/24
3/25
4/3
4/6
4/12
Nuc yard(s)
Create a spreadsheet to keep track of dates
Vaporization
(Sublimation)
A Magic Wand?
http://www.thekidsmovies.com/movies/showmovie/xtsfgm-OKSALK-AST-BUHARLATIRMA-APARATI-OXALC-ACD-VAPORZER-DENEME-GRNTLER
Useful where winter comes on suddenly.
Simple Varrox vaporizer.
http://www.dailymotion.com/video/xm2z06_oksalik-asit-buhariyla-varroamucadelesi-oxalic-acid-vaporizer_animals
Vaporized oxalic is dangerous!
Wear a respirator.
Other issues:
Cooked bees
Burnt wood or plastic
https://beeinformed.org/2014/02/03/oxalic-acid-fogger-demostration/
Sublimation may be
easier on the bees.
Soon to be published
Dribble vs. Sublimation
Dribble
Pros:
Sublimation
High efficacy
Perhaps higher efficacy
Very safe to apply
No opening of the hive
Quick
Pros:
Little equip needed
Can do in freezing weather
Perhaps gentler to the bees
No syrup mixing
Requires opening hive
Cons:
May be problematic in
freezing weather
Easier with helper
Vapor fog is hazardous
Cons:
Requires specialized vaporizer
and energy source
Problems with hot tip
Another application
method
Oxalic/glycerine on cardboard strips.
A Critical Closing Thought
“The only way to halt the development of
resistance to a certain product is by interrupting
its use in the control strategy.”
Lodesani (2009) Limits of chemotherapy in beekeeping: development of resistance and the
problem of residues.
Practice some sort of rotation of treatments
Formic
Amitraz
Oxalic
Thymol
Bloom Honey Co
Bloom Honey Co
Happy beekeeping!
ScientificBeekeeping.com